clarify installation instructions.
clarify installation instructions.

I encounted an error on building due to a missing `tools.jar` because I had JRE but not the JDK
wanghaisheng/clinical_quality_language-Research,cqframework/clinical_quality_language,MeasureAuthoringTool/clinical_quality_language,cqframework/clinical_quality_language,MeasureAuthoringTool/clinical_quality_language,MeasureAuthoringTool/clinical_quality_language,wanghaisheng/clinical_quality_language-Research,wanghaisheng/clinical_quality_language-Research,MeasureAuthoringTool/clinical_quality_language